图形学复习笔记
15:35 2019/10/18
反射，折射的推导
18:23 2019/10/18
bezier curves 与 bezier spline的区别
bezier curves 曲线
bezier spline 样条 或 样条曲线，是由多段bezier曲线平滑连接而成的(共用端点控制点）
22:14 2019/10/18
Graphics中，用Matrix把点从一个空间转换至另一个空间是比较常见的操作，如把World Space Position转换到View Space。但是对于NonOrthogonal matrix（非正交矩阵）来说，转换之后的Normal就不垂直于它的Tangent了。
gl_NormalMatrix
https://www.cnblogs.com/bigdudu/articles/4191042.html
17:42 2019/11/18
注意，列优先矩阵 m4x3表示4列3行，而不是4行3列
列优先矩阵M,点P相乘: Q = MXP，运算时是拿M的行乘列向量P，而不是拿M的列乘行向量P
这个说明在OPENGL系列中，向量默认是列向量
GL_TEXTURE_MIN_FILTER 纹理缩小（镜头拉远）时采用的过滤（点采样) 方式
GL_TEXTURE_MAG_FILTER 纹理放大（镜头拉近）时采用的过滤方式
22:10 2019/11/19
可变不可变纹理，体现在如何对它存储数据上
可变纹理使用 glTexImage2D 来上传数据
不可变纹理使用 glTexStrage2D 来上传数据
10:35 2019/11/22
glUniformMatrix4fv(loc, count, GL_FALSE, addr)
glUniform4fv(loc, count, GL_FALSE, addr)
注意：
一，glUniformMatrix4fv表示的是一个4X4矩阵
glUniformMatrix3fv表示一个3X3矩阵
glUniformMatrix4X3fv表示一个4X3矩阵（4列3行）
二，对于matrix类型，count是指矩阵数量，对于非矩阵类型，count是指向量的个数，例如：
float vec[4] = float[4]{1,2,3,4}
gluniform4fv(1, 1, gl_false, vec)，表示1一个4元素数据
10:42 2019/11/22
PCF的原文在这里，基于阴影图的模糊算法是PCF的变体
----real time renderring 4----------------------------------------
7.5 Percentage-Closer Filtering
A simple extension of the shadow-map technique can provide pseudo-soft shadows.
This method can also help ameliorate resolution problems that cause shadows to
look blocky when a single light-sample cell covers many screen pixels. The solution is
similar to texture magnification (Section 6.2.1). Instead of a single sample being taken
off the shadow map, the four nearest samples are retrieved. The technique does not
interpolate between the depths themselves, but rather the results of their comparisons
with the surface’s depth. That is, the surface’s depth is compared separately to the
four texel depths, and the point is then determined to be in light or shadow for
each shadow-map sample. These results, i.e., 0 for shadow and 1 for light, are then
bilinearly interpolated to calculate how much the light actually contributes to the
surface location. This filtering results in an artificially soft shadow. These penumbrae
change, depending on the shadow map’s resolution, camera location, and other factors.
For example, a higher resolution makes for a narrower softening of the edges. Still, a
little penumbra and smoothing is better than none at all.
This idea of retrieving multiple samples from a shadow map and blending the
results is called percentage-closer filtering (PCF) [1475].
